C/C++

Feb

2021

Minimal ESP32 NTP client example using NTPClient_Generic and PlatformIO

main.cpp

#include <Arduino.h>
#include <WiFi.h>
#include <NTPClient_Generic.h>

#define TIME_ZONE_OFFSET_HRS 1 // UTC+1 for Germany, winter time
#define NTP_UPDATE_INTERVAL_MS 60000L // Update every 60s automatically
WiFiUDP ntpUDP;
NTPClient ntpClient(ntpUDP, "europe.pool.ntp.org", (3600 * TIME_ZONE_OFFSET_HRS), NTP_UPDATE_INTERVAL_MS);

void ntpUpdateTask(void* param) {
  while(true) {
    // Update NTP. This will only ACTUALLY update if
    // the NTP client has not updated for NTP_UPDATE_INTERVAL_MS
    ntpClient.update();
    vTaskDelay(1000 / portTICK_PERIOD_MS);
  }
}

void setup() {
  Serial.begin(115200);
  // Force reset Wifi to avoid failure to connect
  WiFi.disconnect(true);
  // Set hostname
  WiFi.config(INADDR_NONE, INADDR_NONE, INADDR_NONE);
  WiFi.setHostname("ESP-NTP");
  // Connect to Wifi
  WiFi.begin("MyWifiSSID", "MyWifiPassword");
  while (WiFi.status() != WL_CONNECTED) {
      delay(100);
      Serial.println("Wifi connecting...");
  }

  // Start NTP client (i.e. start listening for NTP packets)
  ntpClient.begin();
  // Create task to automatically update NTP in the background
  xTaskCreate(ntpUpdateTask, "NTP update", 2000, nullptr, 1, nullptr);
}

void loop() {
  delay(1000);
  if (ntpClient.updated()) {
    Serial.println("# Time in sync with NTP server");
  } else {
    Serial.println("# TIME NOT IN SYNC WITH NTP SERVER !");
    return; // Do not print time
  }

  Serial.println("UTC : " + ntpClient.getFormattedUTCTime());
  Serial.println("UTC : " + ntpClient.getFormattedUTCDateTime());
  Serial.println("LOC : " + ntpClient.getFormattedTime());
}

platformio.ini

[env:nodemcu-32s]
platform = espressif32
board = nodemcu-32s
framework = arduino
monitor_speed = 115200
lib_deps =
    khoih.prog/NTPClient_Generic @ ^3.2.2
    Time

Example output:

Wifi connecting...
Wifi connecting...
Wifi connecting...
# TIME NOT IN SYNC WITH NTP SERVER !
# Time in sync with NTP server
UTC : 01:22:07
UTC : 01:22:07 Sun 07 Feb 2021
LOC : 02:22:07
# Time in sync with NTP server
UTC : 01:22:08
UTC : 01:22:08 Sun 07 Feb 2021
LOC : 02:22:08
# Time in sync with NTP server
UTC : 01:22:09
UTC : 01:22:09 Sun 07 Feb 2021
LOC : 02:22:09

Feb

2021

How to get current gateway IP address on ESP8266/ESP32

In order to get the current gateway IP address on the ESP8266 or ESP32, use:

WiFi.gatewayIP();

In order to print the gateway IP address on the serial port, use

Serial.println("Gateway IP address: ");
Serial.println(WiFi.gatewayIP());

In order to get the gateway IP address as string, use

String gatewayIP = WiFi.gatewayIP().toString();

Feb

2021

ESP32 minimal WebSocket example (ESPAsyncWebserver / PlatformIO)

Minimal firmware to use WebSockets on the ESP32 using ESPAsyncWebserver:

main.cpp

#include <Arduino.h>
#include <WiFi.h>
#include <ESPAsyncWebServer.h>
#include <ArduinoJson.h>

AsyncWebServer server(80);
AsyncWebSocket ws("/ws");

AsyncWebSocketClient* wsClient;
 
void onWsEvent(AsyncWebSocket * server, AsyncWebSocketClient * client, AwsEventType type, void * arg, uint8_t *data, size_t len){
  if(type == WS_EVT_CONNECT){
    wsClient = client;
  } else if(type == WS_EVT_DISCONNECT){
    wsClient = nullptr;
  }
}

/**
 * Wait for WiFi connection, and, if not connected, reboot
 */
void waitForWiFiConnectOrReboot(bool printOnSerial=true) {
  uint32_t notConnectedCounter = 0;
  while (WiFi.status() != WL_CONNECTED) {
      delay(100);
      if(printOnSerial) {
        Serial.println("Wifi connecting...");
      }
      notConnectedCounter++;
      if(notConnectedCounter > 50) { // Reset board if not connected after 5s
          if(printOnSerial) {
            Serial.println("Resetting due to Wifi not connecting...");
          }
          ESP.restart();
      }
  }
  if(printOnSerial) {
    // Print wifi IP addess
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());
  }
}


void setup() { 
  Serial.begin(115200);
  WiFi.config(INADDR_NONE, INADDR_NONE, INADDR_NONE);
  WiFi.setHostname("ESP-Websocket-Test");

  WiFi.begin("MyWifiSSID", "MyWifiPassword");
  waitForWiFiConnectOrReboot();

  // Start webserver
  ws.onEvent(onWsEvent);
  server.addHandler(&ws);
  server.begin();
}

uint64_t counter = 0;
void loop() {
  // If client is connected ...
  if(wsClient != nullptr && wsClient->canSend()) {
    // .. send hello message :-)
    wsClient->text("Hello client");
  }

  // Wait 10 ms
  delay(10);
}

platformio.ini:

[env:nodemcu-32s]
platform = espressif32
board = nodemcu-32s
framework = arduino
monitor_speed = 115200
lib_deps =
    ESP Async [email protected]
    [email protected]

Python code for testing:

import websocket
ws = websocket.WebSocket()
ws.connect("ws://192.168.1.211/ws")
while True:
    result = ws.recv()
    print(result)

This will print Hello Client many times a second.

Feb

2021

How to fix ESP32 too few arguments to function ‘esp_err_t esp_wifi_sta_wpa2_ent_enable(const esp_wpa2_config_t*)’

Problem:

While trying to compile your ESP32 application, you see this compiler error:

src\main.cpp: In function 'void wifiConnectWPAEAP(const char*, const char*, const char*, const char*)':
src\main.cpp:23:32: error: too few arguments to function 'esp_err_t esp_wifi_sta_wpa2_ent_enable(const esp_wpa2_config_t*)'   esp_wifi_sta_wpa2_ent_enable();
                                ^

Solution:

Replace

esp_wifi_sta_wpa2_ent_enable();

esp_wpa2_config_t config = WPA2_CONFIG_INIT_DEFAULT();
esp_wifi_sta_wpa2_ent_enable(&config);

Feb

2021

How to fix ESP32 fatal error: ESP8266WiFi.h: No such file or directory

Problem:

While trying to compile your ESP32 application, you see this compiler error:

fatal error: ESP8266WiFi.h: No such file or directory

Solution:

ESP8266WiFi.h is the Wifi header for the ESP8266. For the ESP32, it’s named WiFi.h. In order to fix the issue, replae

#include <ESP8266WiFi.h>

#include <WiFi.h>

Feb

2021

How to fix Alpine Linux fatal error: stdio.h: No such file or directory

Problem:

When trying to compile a C/C++ program or library on Alpine Linux, you see an error message like

/home/user/test.cpp:5:10: fatal error: stdio.h: No such file or directory
  123 | #include <stdio.h>
      |          ^~~~~~~~~

Solution:

Install the libc headers using

apk add musl-dev

Jan

2021

Minimal ESP8266 WiFi example

#include <Arduino.h>
#include <ESP8266WiFi.h>

void setup() {
  Serial.begin(115200);
  WiFi.begin("MySSID", "MyPassword");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.println("Wifi connecting...");
    delay(500);
  }
  Serial.println("Wifi connected");
}

void loop() {
  // put your main code here, to run repeatedly:
}

Oct

2020

Where to find info about mbed mbed_app.json overridable parameters?

The first resource can have a look at is the platform configuration option page. Additionally, check the manual on how to use the mbed CLI to show configuration options.

Additionally, you can look at targets.json on GitHub:

For example, "Target" => "config" => "default-adc-vref" would need to be entered like this into mbed_app.json:

{
    "target_overrides": {
      "*": {
          "target.default-adc-vref": 3300
      }
    }
}

Oct

2020

How to fix mbed AnalogIn.read_voltage() returning nan or 0.000 (PlatformIO)

Problem:

You are trying to read an ADC voltage in mbed / PlatformIO like this:

AnalogIn myADC(PA_5); 
// Read and print voltage, then return
float v = myADC.read_voltage();
printf("%f\n", v);

but this only prints nan or 0.000.

Solution:

mbed doesn’t know the reference voltage for your platform. The easiest method is to provide the referene voltage in the constructor of AnalogIn:

AnalogIn myADC(PA_5, 3.3);

This specifies a reference voltage of 3.3V. While this applies to most applications in their default configuration, note that the reference voltage might be different depending on the configuration of your microcontroller.

In my experience, it’s almost always better to experimentally verify the reference voltage instead of trying to theorize about it if it’s not immediately obvious.

Full example:

#include <mbed.h>

BufferedSerial pc(USBTX, USBRX, 115200); // tx, rx

AnalogIn   myADC(PA_5, 3.3);

FileHandle *mbed::mbed_override_console(int fd) {
    return &pc;
}

int main() {
  while(1) {
    float v = myADC.read_voltage();
    printf("%f\n", v);
    ThisThread::sleep_for(100ms);
  }
}

{
    "target_overrides": {
      "*": {
        "target.printf_lib": "std"
      }
    }
}

Oct

2020

How to fix mbed printf() ignoring decimals in PlatformIO

Problem:

You are using code like

printf("%.2f\n", myFloat);

in your mbed/PlatformIO application, but instead of printing myFloat with 2 decimal places, it always prints it with 6 decimal places (like 0.000000).

Solution:

mbed uses the minimal-printf library by default which is configured to save space on the Microcontroller. Hence, float max decimals support is disabled by default. In order to get all printf features at the expense of more flash usage and much slower executing, us add mbed_app.json in the root directory of the PlatformIO project with "target.printf_lib": "std":

{
    "target_overrides": {
      "*": {
        "target.printf_lib": "std"
      }
    }
}

See the platform configuration option page for more details and similar options.

Oct

2020

How to fix mbed printf() printing literal %f in PlatformIO

Problem:

You are using code like

printf("%f\n", myFloat);

in your mbed/PlatformIO application, but instead of printing myFloat it prints literal %f.

Solution:

mbed uses the minimal-printf library by default which is configured to save space on the Microcontroller. Hence, float support (i.e. %f support) is disabled by default. You need to enable it by adding mbed_app.json in the root directory of the PlatformIO project with "platform.minimal-printf-enable-floating-point": true:

{
    "target_overrides": {
      "*": {
        "platform.minimal-printf-enable-floating-point": true
      }
    }
}

See the platform configuration option page for more details and similar options.

Jun

2020

mbed STM32 timer interrupt example

You can use the mbed Ticker API to add a timer interrupt to your mbed application. This example will use a Ticker-based timer interrupt to toggle the LED once per second, for example on the STM32F429I-DISCO board:

#include <mbed.h>

DigitalOut led1(LED1);
Ticker ticker;

/**
 * This function will be run once per second
 */
void timerTick() {
  // Toggle LED
  led1 = !led1;
}

int main() {
  ticker.attach(timerTick, 1.0 /* seconds */);

  // What you do in the main loop is not important
  while(1) {
  }
}

Jun

2020

How to fix PlatformIO fatal error: stm32f429i_discovery_lcd.h: No such file or directory

Problem:

You are trying to compile your PlatformIO application using the LCD_DISCO_F429ZI library, but you see an error message like

 #include "stm32f429i_discovery_lcd.h"
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
*** [.pio\build\disco_f429zi\src\main.o] Error 1
In file included from .pio\libdeps\disco_f429zi\LCD_DISCO_F429ZI_ID2432\LCD_DISCO_F429ZI.cpp:19:0:
.pio\libdeps\disco_f429zi\LCD_DISCO_F429ZI_ID2432\LCD_DISCO_F429ZI.h:25:10: fatal error: stm32f429i_discovery_lcd.h: No such file or directory

Solution:

First, ensure that BSP_DISCO_F429ZI is listed is library dependency in platformio.ini like this:

[env:disco_f429zi]
platform = ststm32
board = disco_f429zi
framework = mbed
lib_deps =
    LCD_DISCO_F429ZI
    BSP_DISCO_F429ZI

Replace the line

#include "stm32f429i_discovery_lcd.h"

in LCD_DISCO_F429ZI.h with

#include "Drivers/BSP/STM32F429I-Discovery/stm32f429i_discovery_lcd.h"

Jun

2020

How to fix PlatformIO fatal error: ../Fonts/fonts.h: No such file or directory

Problem:

You are trying to compile a PlatformIO application using the BSP_DISCO_F429ZI library, but you see an error message like

In file included from .pio\libdeps\disco_f429zi\BSP_DISCO_F429ZI_ID2208\Drivers\BSP\STM32F429I-Discovery\stm32f429i_discovery_lcd.c:75:0:
.pio\libdeps\disco_f429zi\BSP_DISCO_F429ZI_ID2208\Drivers\BSP\STM32F429I-Discovery\stm32f429i_discovery_lcd.h:49:10: fatal error: ../Fonts/fonts.h: No such file or directory
 #include "../Fonts/fonts.h"
          ^~~~~~~~~~~~~~~~~~
compilation terminated.

Solution:

The BSP_DISCO_F429ZI package includes fonts.h from the wrong directory. Replace

#include "../Fonts/fonts.h"

#include "Utilities/Fonts/fonts.h"

in order to fix the issue. You might need to do that multiple times (in multiple files) in order to fix your build.

Jun

2020

How to toggle the STM32F429I-DISCOVERY LED using mbed + PlatformIO

This simple firmare toggles the LED on the STM32F429I-DISC1 discovery board.

#include <mbed.h>

DigitalOut myled(LED1);

int main() {
  while(1) {
    myled = !myled;
    wait(0.5);
  }
}

This will toggle the green (PG13) LED twice per second.

The program is simple: We toggle the LED using myled = !myled; and then use wait(0.5) for 0.5 seconds.

Jun

2020

How to fix C/C++ error: call of overloaded ‘abs(uint32_t)’ is ambiguous

Problem:

You are trying to compile a C/C++ program but you see an error message like

src\main.cpp:127:21: error: call of overloaded 'abs(uint32_t)' is ambiguous

that refers to a line like

long timedelta = abs(millis() - startTime);

Solution:

Cast the argument to abs() to int or another suitable type:

long timedelta = abs(((int)millis() - startTime));

That should fix the error.

The reason for the error message is that millis() and startTime are both unsigned integers (uint32_t), hence their difference (millis() - startTime) is also an uint32_t. However it makes no sense to compute the abs() of an unsigned integer since the absolute value of an absolute-value integer is always the same as the input argument.

Then, the compiler tries to cast the uint32_t to any type that is compatible with abs(), like int, float, double, … but it doesn’t know which of those types is the correct one to cast it to.

By saying call of overloaded abs() the compiler is trying to tell you that there are multBiple argument types with which you can call abs(), including int, float, double, … – a function with the same name but different argument types is called overloaded.

By saying is ambiguous, the compiler is telling you that it doesn’t know which of those variants of abs() it should call.

Note that the compiler does not know that all overloaded variants of abs() fundamentally do the same thing, so it won’t just cast your uint32_t into any arbitrary type. Also, there are tiny details in how the abs() variants work – for example, float abs(float) will do a different calculation compared to double abs(double) since it computes with 32-bit floating point numbers (float) as opposed to 64-bit floating point numbers (double).

Hence, the compiler can’t just assume that they are all the same and it doesn’t matter which one it calls, even though they represent the same underlying mathematical operation

Jun

2020

How to fix C/C++ round(): error: invalid operands of types ‘float’ and ‘int’ to binary ‘operator&’

Problem:

You are trying to compile a C/C++ program but you see an error message like

src\main.cpp:357:21: error: invalid operands of types 'float' and 'int' to binary 'operator&'

that refers to a line like

long m = round(v) & 0x7FF;

Solution:

The result of round() is a floating point number. You are trying to use the & operator to perform bitwise AND of a float and an int (0x7FF in the example above). However, you can not perform bitwise operation on floats in C/C++.

In order to fix this, case the result of round() to int:

long m = ((int)round(v)) & 0x7FF;

That should fix the compiler error.

Jun

2020

How to fix Keil EFM8 Warning C280: unreferenced local variable

Problem:

You have a C function like

int myfunc(int value) {
  return 0;
}

but you see a Keil compiler warning like

*** WARNING C280 IN LINE 7 OF C:\Users\uli\MyProject\src\main.c: 'value': unreferenced local variable

Solution:

'value': unreferenced local variable means that you don’t use that variable value in any way.

In the function shown above, you can see that value is the argument of myfunc but myfunc never actually uses the variable.

Do you think that variable should be used in this function?

You need to check your function for typos – the variable is never used at all. Possibly you are using the wrong variable or your function is missing some part of its logic.

Don’t want to use that variable at all?

Usually you can tell the compiler that you don’t want to use that variable by using

(void)value;

but that will produce an expression with possibly no effect warning.

*** WARNING C275 IN LINE 7 OF C:\Users\uli\MyProject\src\main.c: expression with possibly no effect

You can use this hack to avoid this warning:

r = r; // Avoid unused local variable

Apr

2020

Minimal ESP-IDF UART transmit example for ESP32 & PlatformIO

The following example writes the string CAFE to UART continously, waiting for 100ms in between:

#include <driver/gpio.h>
#include <driver/uart.h>
// Include FreeRTOS for delay
#include <freertos/FreeRTOS.h>
#include <freertos/task.h>

int app_main() {
    uart_config_t uart_config = {
        .baud_rate = 115200,
        .data_bits = UART_DATA_8_BITS,
        .parity    = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
    };
    uart_driver_install(UART_NUM_1, 2048, 0, 0, NULL, 0);
    uart_param_config(UART_NUM_1, &uart_config);
    uart_set_pin(UART_NUM_1, 10, 9, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);

    // Main loop
    while(true) {
        uart_write_bytes(UART_NUM_1, "CAFE", 5);
        vTaskDelay(100 / portTICK_RATE_MS);
    }
}

Apr

2020

ESP-IDF equivalent to Arduino delay()

You can use the FreeRTOS API to provide a delay similar to the Arduino delay() function in the ESP-IDF framework. FreeRTOS is included in the PlatformIO ESP-IDF default configuration.

First, include the FreeRTOS headers

// Include FreeRTOS for delay
#include <freertos/FreeRTOS.h>
#include <freertos/task.h>

After that, you can use vTaskDelay(...) to perform the delay. This example delays by 500ms:

vTaskDelay(500 / portTICK_RATE_MS);

You can use vTaskDelay() even if not using FreeRTOS tasks.

For a full example, refer to PlatformIO ESP-IDF ESP32 blink example

main.cpp

platformio.ini

Example output:

main.cpp

platformio.ini:

Python code for testing:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Full example:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Problem:

Solution:

Do you think that variable should be used in this function?

Don’t want to use that variable at all?

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